A high-security lock has more than one bolt that is extended from the door edge into the jamb when the door is locked. These bolts are normally actuated by at least one slide that moves in a standard installation vertically and that is either directly connected to a bolt that can emerge from the top and/or bottom edge of the door or through a linkage to a bolt that emerges from the vertical side edge of the door well above and/or below the lock. Thus in order to lock the door by extending these bolts it is necessary to move a substantial amount of mechanism.
In European patent document 1,454,966 such an arrangement is described which is wholly actuated by the key. A step-down transmission is connected between the rotary part of the key cylinder and the bolt slide. Thus the user of the lock must laboriously crank the key around to lock and unlock the door, subjecting the key to a torsion it was not really meant to withstand.
European patent document 2,391,063 has a system where the bolt slide can be operated by the door handle. The inside handle is biased into a central position and is moved in one direction to lock the door and in the opposite direction to open it. When such a lock is provided with a key mechanism it becomes fairly bulky and complex, and when locked it cannot be opened from inside even in an emergency.